Electric heaters



J. F. VOLKER ELECTRIC HEATERS July 21, 1970 INVENTOR. JoHN F VOLKER I5 Sheets-Sheet 1 L@ mw .NTH

Qm- NWN Filed Aug. '26. 1968 MMM/wf July 2l, 1970 J. F. voLKER ELECTRIC HEATERS Filed Aug. 26. 1968 3 Sheets-Sheet 2 INVENTOR. JQHN F. VOLKER BY I ze July 21, 1970A J. F. voLKER i 3,521,352

ELECTRIC HEATERS Fned Aug. ze, 196e s sheets-sheet s u INVENTOR. JOHN F. VOLKER A T TURA/@f5 UnitedStates Patent O 3,521,352 ELECTRIC HEATERS John F. Volker, Pittsburgh, Pa., assignor to Emerson Electric Company, St. Louis, Mo. Filed Aug. 26, 1968, Ser. No. 755,297 Int. Cl. Hb 3/00 U.S. Cl. 29-611 8 Claims ABSTRACT OF THE DISCLOSURE An electric heater comprising a terminal section including a terminal rod disposed in electrically-insulated concentric relation within a metal tube, and a pair of concentric coiled resistors, the outer resistor having an end electrically connected to the tube and the inner resistor having an end electrically connected to the terminal rod. The terminal section, with attached resistors, are then disposed in coaxial relation within a tubular metal shea-th and refractory material is inserted within the sheath for electrical insulation. The sheath is hermetically sealed at one end by a plug welded in to the sheath, and at the other end by a terminal housing which is welded to the sheath. The terminal housing contains electrical connections with the terminal rod and metal tube, and such connections include looped portions to accommodate eXpansion and contraction.

BACKGROUND AND SUMMARY Electric heaters of the type shown in McOrlly Pat. 3,087,134 have been found to be extremely reliable in operation in uses where durability and dependability are required. As the size and capacity of the heaters are increased in accordance demands, the construction of the patented heaters required change, and the present invention provides a heater construction which permits the incorporation of the desirable qualities of the patented heaters in larger sizes and capacities.

DESCRIPTION OF THE DRAWINGS In the drawings accompanying this description and forming a part of this specication, there is shown, for purposes of illustration, an embodiment which my invention may assume, and in this drawing:

FIG. 1 is a broken sectional view through the terminal section of the heater,

FIG. 2 is a view similar to FIG. 1 but after a side pressing operation, and further showing the connection of the heating resistors,

FIG. 3 is a fragmentary enlarged section showing the electrical interconnection of the free ends of the heating resistors, and the assembly of a centering plug,

FIG. 4 is a section corresponding generally to the line I 4--4 of FIG. 3,

FIG. 5 is a broken sectional view illustrating the assembly of the construction of FIGS. 2 through 4 within a metal sheath, prior to a filling operation,

FIG. 6 is a broken sectional view of the parts shown in FIG. 5 but after lling the side pressing and certain machining operations,

FIG. 7 is an enlarged, broken sectional view showing the electric heater in final assembly,

FIG. 8 is a fragmentary sectional view of a detail of the construction shown in FIG. 7, and

FIGS. 9 and 10 are perspective views of parts used in the assembly shown in FIG. 7.

DETAILED DESCRIPTION The terminal rod section 10 of the heater is formed as a separate assembly, and comprises a metal tube 11 and 3,521,352 Patented July 21, 1970 a terminal rod 12. The terminal rod 12 has a connector portion 14 at one end, for connection to the spline of a conventional filling machine. A mica bushing 15 is disposed in one end of tube 11 to close this end, and the tube is uprighted with the bushing 15 lowermost, and placed in the filling machine for the operation which lls the space between the terminal rod 12 and the interior of the tube 11 with powdered refractory material 151 in known manner. As is well known in the art, the filling operation provides a certain degree of compactness to the refractory material.

After the tube 11 has been filled with refractory material, it is removed from the filling machine and a mica plug 16 is inserted within the upper end of the tube so that the latter may be handled and worked without loss of refractory material. Instead of powdered refractory material, a series of refractory bushings may be inserted Over the terminal pin to occupy the space between the pin and tube interior, and the filling machine operation may thus be eliminated.

The assembly thus produced is side pressed to further compact the refractory material. Then, the connector portion 14 is cut off, and step-down or neck portions 17 and 18 are machined on the tube 11 and terminal rod 12, respectively.

The heating resistors comprise outer and inner coils 19 and 20, each preferably formed of a suitable metal ribbon which is wound spirally. One end of the outer coil has an internal diameter to fit closely over the neck portion 17 of the tube 11 (see FIG. 2) and one end of the inner coil 20 has a internal diameter to fit closely over the neck portion 18 of the terminal rod 12, and such end portions are welded to the neck portions, such as by a heliarc weld.

The coils 19 and 20 are preferably of constant diameters and the coil 20 is disposed concentrically within the coil 19, as shown. The opposite end (right hand end in FIG. 2) has a conical formation 19e to t closely over a conical metal plug 21, as best seen in FIG. 3, and is welded to the plug. The plug 21 is formed with a central longitudinal opening 22 to receive the adjoining end of the inner coil 20 so that the coils at this end are held in concentricity. The plug 21 is also formed with a peripheral undercut 23 and a transverse opening 24 is provided so that a weld 25 may be made between the plug 21 and the inner coil 20. The plug 21 is formed with a central threaded opening for a purpose later to appear.

A centering bushing 26 is disposed over the conical end of the outer coil 19, the bushing having its periphery formed with longitudinal grooves, as shown at 27, and having a center opening 28. The bushing 26 is formed of an electric insulating material such as Alsimag 714 or equivalent, since it is required to be of a crushable nature, yet red to produce sufficient hardness to prevent breakage from normal handling.

'The assembly thus far produced is placed within an outer tubular metal sheath 29, as shown in FIG. 5. Ceramic bushings 30 are disposed over the tube 11 to lill the space between the tube 11 and sheath 29, the bushings 30 preferably ending at the neck portion 17 of the tube 11. A ceramic bushing 31 is disposed over the outer coil 19 and between this coil portion and the interior of sheath 29. A further ceramic bushing 32 is disposed between the coils 19 and 20. The bushings 31 and 32 insure that the coils are electrically insulated at this point.

The assembly is now ready for receiving powdered refractory material to fill the space within the sheath 29 and around and between the coils 19 and 20. Preparatory for the filling operation, an upper tilling machine plug 35 is assembled with the right hand end (FIG. 5) of the sheath 29. The plug includes a shank 36 which has an end threaded into the plug 21. A closure disc 37 is threaded onto the shank 36 and seats on the end of the sheath 29. The disc 37 may be rotated on the shank to establish a desirable tension on the inner and outer coils 20 and 19 and thus hold them in separated, concentric relation. The disc is apertured as at 38 to pass the refractory material, and bushing grooves 27 also accommodate this function. It will be noted that the metal tube 11 and terminal rod 12 will withstand a heavy pull on the resistor coils, and such pull is necessary due to the size of the coils.

A lower filling-machine plug 39 is connected t0 the left hand end (FIG. 4) of the sheath 29, and closes the opening into the sheath. The plug 39 has a tubular portion 40 which fits into the space between the tube 11 and sheath 29 to maintain the same in concentric relation. The left end of the terminal rod 12 projects through an opening 41 in the plug and set screws (not shown) are threaded into apertures 42 to engage the rod and hold it centered.

The foregoing assembly is then placed within a conventional filling machine in upright position and powdered refractory material 42a is caused to flow through the openings 38 in the upper plug 35 to ll the open spaces in the sheath 29. This material will flow through the grooves 27 in the centering bushing 26 and, starting from the bushing 31 and working upwardly to the plug 35, will ill all cracks and crevises within the sheath 29, and indeed may filter downward to ll any small spaces between the ceramic bushings 30 and adjoining sheath surfaces. The lilling operation is accompanied by a vibratory action to assist in compactly filling all spaces.

After the filling operation, the top closure 35 is removed and a plastic bushing (not shown) is rammed in place to close the end of sheath 29. The assembly is then turned end for end and the bottom closure 39 is removed and a plastic bushing (not shown) is rammed in place to close this end of the assembly. The assembly is then subjected to a side pressing operation to compact the powdered refractory material 42a to a rock-like density. The side pressing operation also crushes the bushings 26, 30, 31 and 32 to powdered but rock-like density, and by reducing the transverse size of the asembly, insures that all cracks and crevices are filled with insulation material. It should be noted that the conical plug 21 holds against any reduction of the dielectric spacing between the inside diameter of the sheath 29 and the outside diameter of the outer coil 19. After the side pressing operation, the ends of the assembly are machined, as shown in FIG. 6, to remove the portions indicated in dotted lines and to bevel the left hand ends of the tube 11 and sheath 29, as shown respectively at 44, 45. Refractory material from the right hand end (FIG. 6) of the sheath 29 is removed and mica discs 46 and a metal plug 47 are inserted with the plug peripherally welded to the sheath as shown at 48 to form a hermetic seal.

The heating unit is now ready for nal assembly operations. Referring to FIG. 7, the refractory material is removel from the left end of the tube 11 and sheath 29 and ceramic bushings 50, 51 are cemented in the spaces thus provided.

An electrical connector 52 and a semi-circular hub 53 (see FIGS. 7 and 9) which is welded to the tube 11 at 54. The hub is semi-circular to enable its installation behind the enlarged head of the bushing 50, since this bushing is already cemented in place. An expansion loop 55 is integral with the hub and extends therefrom and terminates in a iiat tail 56. An electrical connector 57 has a portion 58 which is apertured as at 60, to pass the end f the terminal rod 12, the portion 58 being connected to the rod by a weld 61. An expansion loop 62 is integral with and extends from the portion 58 and terminates in a at tail 63.

Either before or after welding of the connectors 52 and 57 to the tube 11 and terminal rod 12, respectively, terminals 64, 65 are brazed to respective tails 56, 63, The terminals are similar and only the terminal 64 is shown in detail in FIG. 8. This terminal extends through and is hermetically sealed to an elongated dielectric sleeve 66 which may be formed of ceramic or other rigid, temperature resistance, insulating material. An apertured cupshaped metal member 67 is suitably bonded to the eX- terior of one end of the sleeve and is circumferentially brazed or otherwise suitably secured at 68 to the portion of the wall 69 of a coupling 70. A cup-shaped metal member 71 is bonded to and over the other end of the sleeve 66.

VSince the coupling 70 is already in assembled relation, a large metal sleeve 72 is inserted over the right hand end (FIG. 7) of the heater assembly and moved along the sheath to the left until it meets the coupling 70, and is joined to the latter by the mutual engaging screwthreads 73. The two parts 70, 72 are threaded to completely seat the threads home, and then Unthreaded about one turn to allow for expansion. The parts 70, 72 are then Welded together 'by the peripheral weld 74 to hermetically seal their interconnection. The nose end 75 of the sleeve 72 is then welded to the sheath 29 by a peripheral weld 76, to hermetically seal their interconnection. In forming the Welds 74, 76 considerable heat is generated causing considerable longitudinal expansion of the parts. Since the conductors 64, 65 are brazed to the coupling 70 and respective connectors 52, 57, the terminal assembly is submitted to longitudinal stress during the welding operations. However, since the connectors 52, 57 have expansion loops therein, no harm is done to any critical connection since the expansion loops absorb expansion and contraction forces.

The sleeve 72 is formed with an opening 77 and powdered refractory material 78 is introduced, under pressure, through this opening to completely fill the space within the sleeve 72 and coupling 70. The opening is then hermetically sealed with a plug weld 79. A dielectric bushing 80 is then disposed over the projecting prongs 81 of the conductors 64, 65 to electrically insulate the same from the coupling 70, and terminal clips 82 are brazed at 83, to the prongs to hold the bushing 80 is place. A rubber boot 84 is disposed around the bushing 80 and surrounds the clips 82 to protect the electrical connections against grounding.

I claim:

1. The method of making an electric heater, comprising forming a terminal assembly for the heater by concentrically disposing a metal conductor rod within a metal conductor tube and compacting refractory insulation between the outer surface of the rod and the inner wall of the tube, with an end of the rod extending outwardly of an end of the tube, machining undercut surfaces on the rod and tube ends to closely receive the ends of two concentrically arranged coiled resistors and mechanically and electrically connecting the resistor ends respectively to the undercut rod and tube surfaces by a fusion joint, electrically interconnecting the other ends of the concentrically arranged resistors, disposing the assembly thus produced concentrically within a metal sheath, and filling the space between said assembly and the inner wall of the metal sheath with refractory material.

2. The method of making an electric heater, comprising forming a terminal assembly for the heater by concentrically disposing a metal conductor rod within a metal conductor tube and compacting refractory insulation between the outer surface of the rod and the inner wall of the tube, with an end of the rod extending outwardly of an end of the tube, closely titting the ends of two concentrically arranged coiled resistors over respective ends of the rod and tube and mechanically and electrically securing the same, disposing the other end of the inner resistor closely within an aperture in a metal conductor plug and closely disposing the other end of the outer resistor over the outer wall surface of the plug and mechanically and electrically securing such resistor ends to the plug, disposing the assembly thus produced concentrically within a metal sheath, and filling the space between said f assembly and the inner wall of the metal sheath with refractory material.

3. The method of claim 2 and including the step of holding the coiled resistors in concentric relation by pulling on said plug in a direction away from said assembly during the filling of said sheath.

4. The method of making an electric heater, comprising forming a terminal assembly for the heater by concentrically disposing a metal conductor rod within a metal conductor tube and compacting refractory insulation between the outer surface of the rod and the inner wall of the tube, with opposite ends of the rod extending outwardly of opposite ends of the tube, closely tting the ends of two concentrically arranged coiled resistors over adjoining ends of the rod and tube at one end of the tube and mechanically and electrically securing the same, mechanically and electrically connecting the opposite ends of the resistors, disposing the assembly thus produced concentrically within a metal sheath, locking the end of the rod at the other end of the tube againstmoevment relative to one end of the sheath, and pulling on the connection at the opposite ends of the resistors in a direction outwardly of the other end of the sheath to maintain said resistors taut and in concentric relation with each other and with the inner wall of the sheath, and filling the space between said assembly and the inner wall of the sheath with refractory material while the resistors are maintained in taut relationship.

5. The method of claim 4 including the step of disposing said opposite other end of the inner resistor closely within an aperture in a metal conductor plug and disposing said opposite end of the outer resistor over the outer wall surface of the plug and mechanically and electrically securing such resistor ends to the plug to form said electrical connection between said opposite ends of the resistors, and pulling on said plug to maintain said resistors taut.

6. The method of claim 4, further including the steps of hermetically sealing both ends f the sheath, the seal at the sheath end adjacent to said assembly including a pair of terminals electrically connected respectively to said rod and tube and adapted to be connected to a power source.

7. The method of claim 6 and further including the step of interposing expansion joints in the electrical connection between the said terminals and their respective connection with said rod and tube.

8. The method of making an electric heater, comprising' first forming a terminal assembly for the heater by concentrically disposing a metal conductor rod within a metal conductor tube and compacting refractory insulation between the outer surface of the rod and the inner wall of the tube, with opposite ends of the rod extending outwardly of opposite ends of the tube, closely fitting the ends of two coucentrically arranged coiled resistors over adjoining ends of the rod and tube at one end of the tube and mechanically and electrically securingthe same, mechanically and electrically connecting the opposite ends of the resistors, disposing the terminal assembly thus produced coucentrically within a metal sheath with the opposite end of the tube and its projecting rod at one end of said sheath and the electrically interconnected ends of the resistors at the other sheath end, lling the space within the sheath with refractory material, hermetically sealing said other sheath end, electrically connecting a thermal expansion member to the end of said rod and the end of said tube at said sheath one end, electrically connecting terminals to respective expansion members, said terminals being adapted for connection to a power source and extending in hermetically seaed relation through the transverse end of a metal coupling having screw threads at one end, inserting a threaded metal sleeve over the hermetically sealed end of the sheath and moving the sleeve along said sheath and threading it to said coupling, welding said coupling and said sleeve at their threaded joint and welding the sleeve to said sheath to provide hermetically sealed connections, forcing powdered refractory material through an opening in said sleeve and into the space within said coupling and sleeve to ll the same, and welding shut said sleeve opening.

References Cited UNITED STATES PATENTS 2,009,980 7/1935 Abbott 338-241 2,494,333 1/1950 Daly 338-239 2,962,683 11/ 1960 Jakubowski 29-619 X FOREIGN PATENTS 494,024 6/ 1953 Canada. 670,557 9/ 1963 Canada.

JOHN F. CAMPBELL, Primary Examiner r V. A. D. PALMA, Assistant Examiner U.S. Cl. X.R. 

